[Me2Si(Me4CF)NtBu]TiCl2 (Constrained-Geometry Catalyst, hereinafter, will be abbreviated as CGC) was reported by Dow Co. in the early 1990s (U.S. Pat. No. 5,064,802), and excellent aspects of the CGC in the copolymerization reaction of ethylene and alpha-olefin may be summarized in the following two points when compared to commonly known metallocene catalysts.
(1) At a high polymerization temperature, high activity is shown and a polymer having high molecular weight is produced, and
(2) the copolymerization degree of alpha-olefin having large steric hindrance such as 1-hexene and 1-octene is excellent.
Meanwhile, a copolymer prepared by using the CGC catalyst includes a small amount of a low molecular weight part and may have improved physical properties such as strength when compared to a copolymer prepared by using a common Ziegler-Natta catalyst.
However, despite the above-described merits, the copolymer prepared by using the CGC catalyst has the defects of deteriorating processability when compared to the polymer prepared by using the common Ziegler-Natta catalyst.
U.S. Pat. No. 5,539,076 discloses a metallocene/non-metallocene blend catalyst system for preparing a specific bimodal copolymer having high density. The catalyst system is supported by an inorganic carrier. A supported Ziegler-Natta catalyst and a metallocene catalyst system have a drawback such that a supported hybrid catalyst has lower activity than a homogeneous single catalyst, and the preparation of an olefin-based polymer having appropriate properties according to the purpose is difficult. In addition, since the olefin-based polymer is prepared in a single reactor, it is apprehended that gel that is generated during a blending process may be produced, the insertion of a comonomer in a high molecular weight part may be difficult, the shape of a produced polymer may become poor, two polymer components may be mixed nonhomogeneously, and the control of quality may become difficult.
Thus, the development of an olefin-based polymer that may overcome the drawbacks of a common olefin-based polymer and provide improved physical properties is still required.